Move from arthurkushman/querypath to GravityPDF/querypath

This seems to have no negative impacts on the tests so marking as ready for review.

Testing this MR locally, the unit tests are passing successfully on Drupal 10.2 / PHP 8.3:

> ./vendor/bin/phpunit -c phpunit.xml web/modules/dev/feeds_ex/tests --bootstrap=/var/www/html/web/core/tests/bootstrap.php
PHPUnit 9.6.19 by Sebastian Bergmann and contributors.

Testing /var/www/html/web/modules/dev/feeds_ex/tests
...............................................................  63 / 113 ( 55%)
..................................................              113 / 113 (100%)

Time: 04:35.271, Memory: 14.00 MB

OK (113 tests, 1189 assertions)

Switching libraries also requires updating Ludwig → integration and the README, so I did just that in the commit.
I also checked if a feed with the QueryPath XML parser worked on a Drupal 10 site when the library gravitypath/querypath was installed with Ludwig.

Probably ready for commit, if tests still pass.

Alright! Merged the changes.

Automatically closed - issue fixed for 2 weeks with no activity.